I think a first step to avoid exploitation is to be aware of and challenge our assumptions. Your observation is that the picture showed homelessness, hopelessness… it might very well show homelessness but if we assume the hopelessness then we are placing our interpretation of the events on the other person. If we do that we are only a step away from then trying to take charge of their life and we begin to cross the line. This person may be hopeless or he might see himself as free. Certainly, he looks uncomfortable but beyond that be careful of making assumptions. Hear the story first then decide what the situation is.